1. Field of the Invention
The present invention relates to a VoIP terminal which, specially relates to a Public Switch Telephony Network (PSTN) connectable VoIP terminal.
2. Description of the Prior Art
With the progress of the Voice over IP (VoIP) technology, more and more Internet voice service applications are developed. FIG. 1A and FIG. 1B illustrate two conventional Internet voice service systems. Referring to FIG. 1A, both sides of the conversation are communicated through the Internet, in which the most common is the conversation between two computers. For example, the computer could transform voice signals into network packets and transmit to another side of the conversation according to telephone software and microphone device. FIG. 1B illustrates the system architecture for wideband phone that a common city telephone connects to the Internet and transmits voice data to foreign subscribers through the Internet instead of the original PSTN. The terminal apparatus of the subscriber A (i.e., wideband phone) includes a modem, which dials on ISP through PSTN first for connecting to the Internet, and then connects to subscriber B or C. In the example, the terminal apparatus of subscriber B is a computer and terminal apparatus of subscriber C is a common city telephone.
With a comparison to the voice services based on a circuit switch network (i.e., PSTN), the fee for Internet conversation is much cheaper and very attractive for business.
The conventional PSTN phone system is a common battery system; it is unnecessary of providing additional power to the terminal apparatus (phone set), except that from telecommunication central office. On the other hand, it is essential to provide power to the terminal apparatus for the Internet voice service. Therefore, the subscriber cannot make a phone call if local subscriber encounters a power off condition. Besides, every established connection of the circuit switch network is monopolistic. Both sides of conversation share and occupy a unique telephone line during conversation as well as a private line except when the connection is unable to establish. As to the Internet connection, different users or applications may share any link section of connection simultaneously. Hence, if a link section is congested, two sides of conversation will receive delayed voices. Furthermore, a circuit switch network such as PSTN is more widely laid. These advantages mentioned make the conventional telephone remain its value and market.
Hence, when a subscriber has the communication environment for connecting to both Internet and PSTN at the same time, it would be better to have a terminal apparatus capable of establishing conversation through Internet and PSTN.